LT4869B - Process for obtaining catalytic composite coatings - Google Patents

Abstract

The invention is in the field of a manufacturing method for compositional catalytic surfaces, when the surface is formed by spraying a molten substance and can be used in various fields - chemical industry, energetics, ecology and other spheres for different catalytic elements, that would enable the chemical industry, metallurgy, thermal power plants, gas pumping stations, internal combustion engines, diesel and stationary power plants to neutralise their exhaust gases. The composite catalytic surface is made by plasmic spraying of the powder mix at the component ratio in mass percentage: metal aluminium and/or titanium 1-7, aluminium and/or titanium oxides 0.1-12, transition metal oxides 1-30, aluminium and/or titanium hydroxide - the remaining amount. Vanadium, chromium, molybdenum, wolfram, manganese, iron, cobalt, nickel and copper oxides are used as transition metal oxides here. The dispersion of the new powder mix is not less than 100 microns. The invention makes it possible to obtain surfaces with good catalytic properties - full conversion of carbon dioxide takes place at not more than 300 degrees C, and the catalyst burning point - the activity indictor of the catalyst - is in the range of 150-180 degrees C.

Description

The process for the preparation of the composite catalytic coating is carried out by the method of plasma spraying of the powder mixture on the substrate with the following composition by weight:

metal aluminum and / or titanium 1-7 aluminum and / or titanium oxides0,1-12 transition metal oxides 1-30 aluminum and / or titanium hydroxides remaining

Oxides of vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper are used as transition metal oxides. The resulting mixture has a powder dispersion of at least 100 microns.

The present invention provides coatings with good catalytic properties on solid substrates - the temperature of the complete conversion of carbon monoxide does not exceed 300 ° C and the ignition temperature of the catalyst, which can be read as a characteristic of catalyst activity, is in the range of 150-180 ° C.

The invention relates to processes for the preparation of composite catalytic coatings, wherein the coating is formed by spraying molten materials on a substrate and can be used in a variety of chemical industries, energy, ecology and the like. in the fields of catalytic cells of various types, which would ensure the neutralization of exhaust components of the chemical and metallurgical industry, of thermal stations, of gas pumping stations, as well as of combustion engines of motor vehicles and of diesel and stationary energy devices.

Methods of thermal coating by gas spraying on metal or ceramic substrates using compositions based on aluminum compounds are known. Aluminum-based alumina is most widely used as a powder for spraying composite coatings (see Metallic and Ceramic Coatings. Production, High Temperature Properties and Application. M. G. Hocking, V. Vasantasree and P. S. Sidky. Materials Department, Imperial College, London 1990).

A known method of forming coatings (see former USSR Authorization No. 2026890, IPC C 25 D, 1992), comprising depositing a backing substrate of an alloyed Zn - Cu - Al - B alloy system followed by a backing layer based on aluminum compounds, containing Al, Cu, Mg, Mn, which is then oxidized by a microwave in an alkaline electrolyte.

The techniques listed above are quite complex, requiring labor-intensive and additional labor-intensive operations: application of the substrate, oxidation or constant temperature control of the substrate and coating.

Known method for obtaining a multilayer coating (see former USSR Authorization No. 2049827, IPC C 23 C 4/00, 1995}, comprising spraying a layer in an inert gas with a dissociated hydrogen additive. Powder that forms hydrated forms of alumina in an inert gas with hydrogen ion additive The base coat is sprayed using an aluminum or nickel composite powder or mixtures thereof and a chemically inert additive with a layered structure such as boron nitride or carbon. containing aluminum, hydrated forms of aluminum hydroxide (such as gibbsite and / or bemite) and boron nitride or carbon additives, which are solid lubricants and provide resistance to wear.

The disadvantages of this method are that the resulting coating is quite expensive due to the large number of intermediate operations and expensive materials used for spraying, such as aluminum nickel powder. In addition, the coating does not have a sufficiently high resistance to wear and porosity, which renders it unsuitable for use as a base for impregnating various mixtures, e.g. neuniversal.

The closest known (prototype) method of preparing composite coatings (see Patent No. 4456 of the Republic of Lithuania, IPC C 23 C 4/00, 1997), wherein the oxide and metal binder containing the porous coating is deposited on the initial substrate by plasma spraying. uses as a starting material for plasma spraying a powder mixture containing aluminum and / or titanium oxides, aluminum and / or titanium hydroxides, as a material forming coating macrostructure glass powder as a material providing a microstructure of the coating and metal aluminum and / or titanium as a metal bond, component composition,% by weight:

metal aluminum and / or titanium 1-7 oxides of aluminum and / or titanium 0.1-12 glass powder 2-45 aluminum and / or titanium hydroxides remaining quantity The dispersion of the powder must be: aluminum and titanium oxides less 30 pm aluminum and titanium hydroxides less 20 pm glass powder less 30 pm aluminum and titanium less 50 pm

The disadvantages of this method are that although the coating produced by this method has sufficiently high adhesion properties of the sprayed layer to the substrate, homogeneous phase composition and large free surface after heat treatment, the catalytic properties are very insignificant.

The object of the present invention is to provide a solid support catalytic layer with pronounced catalytic properties.

The object is achieved by blending transition metal oxides (vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper) in the form of a single component of the composition, namely hydroxide, in a known manner to obtain a composite coating, either alone or in a mixture. for the following composition of components,% by weight:

Aluminum and / or titanium metal 1 - 7 Oxides of aluminum and / or titanium 0,1-12 Oxides of transition metal 1 - 30 Hydroxides of aluminum and / or titanium

From the description of the prototype, it can be seen that the coating obtained by this technology can be further used for anti - corrosion coatings on metals and polymers, anti - friction coatings, varnish - paint coatings and coatings with special properties, including coatings with catalytic properties.

This coating can certainly have minor catalytic properties since the fused aluminum and titanium hydroxides after thermal treatment have to produce γ-modified alumina and anatase-modified titanium oxides which have some catalytic properties in the exhaust gas components such as carbon monoxide. , in oxidation and reduction reactions. However, the catalytic activity of said oxides is usually so low that it is never used as a catalyst, but is practically always used as a catalytic carrier on which the catalyst is deposited in various ways. Commonly used methods are impregnation with various salts, with subsequent drying and thermal decomposition of salts, sol-gel methods, gaseous chemical precipitation methods, magnetron or ion plasma spraying and other methods.

Catalysts usually include precious metals - platinum, palladium, rhodium, sometimes gold or silver, or metal oxides - iron, copper, nickel, cobalt, vanadium, tungsten and others. oxides.

Catalysts in the form of metal oxides are widely used in various processes in the chemical industry as well as in the decontamination of exhaust gases. As a catalytic carrier, ceramic carriers are usually used as spinel, zeolites or others. type complex oxides. In addition, they usually contain aluminum oxide.

For example, a known catalyst for the methanol synthesis process (see U.S. Patent No. 5767039, TPK B 01 J 23/06, B 01 J 23/72, June 16, 1998). This synthetic catalyst is based on oxides of aluminum, copper and zinc, by mixing copper and zinc with subsequent precipitation together with aluminum from its salts.

A complex catalyst for the neutralization of nitrogen oxides is also known (see U.S. Patent No. 5,776,426, TPC C 01 F 1/00, B 01 D 11/00, July 7, 1998). It is a zeolite-type catalytic carrier with embedded active centers based on copper, cobalt and iron ions. The catalytic material contains 2 - 8% copper, 1 - 4% iron and 0.25 - 4% cobalt.

Also known is a catalyst for the production of methylethylketone on the basis of copper and silicon oxides (see U.S. Patent No. 5,723,679, IPC C 07 C 45/001998 03 03).

Spinel (complex oxide based on alumina) containing copper and zinc ions (see U.S. Patent No. 5,750,460, TPK B 01 J 23/06, B 01 J 21/04, B 01 J) is used as a catalyst for the single reduction of copper oxides and the oxidation of hydrocarbons. 23/72, 12 May 1998).

Thus, in order to obtain a catalytic coating with high catalytic properties, a thin monomolecular catalyst layer must, as a rule, be applied to the coating obtained according to the prototype described.

However, as the studies have shown, the catalyst can be introduced into the catalytic layer and in the plasma carrier stage of the catalyst carrier. In this case, one of the components of the spray composition, namely the hydroxide, is mixed with an oxide powder of dispersed transition metals (vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper) singly or in combination.

The method is implemented as follows:

The composite coating is sprayed on a solid metal or ceramic substrate. An aluminum hydroxide powder formulation with the following composition by weight was used:

metal aluminum and / or titanium aluminum and / or titanium oxide

1-7 0,1 -12 transition metal oxides 1 - 30 aluminum and / or titanium oxide remaining

Prior to spraying, the powder formulation is activated in a ball mill according to a specific mode which, due to the adhesion of the aluminum hydroxide particles to the oxide particles, produces a dispersed (at least 100 sec) powder composition with fine oxide particles on the surface of sufficiently large hydroxide particles.

An example.

Composite coating was sprayed on a substrate made of 40 microns thick steel. An aluminum hydroxide powder formulation with the following composition by weight was used:

metal aluminum - 6 vanadium oxide - 2 chromium oxide - 4 molybdenum oxide - 3 tungsten oxide - 3 aluminum hydroxide - remaining

The plasmidron PN-V1 with separate powder component feed and the APR-403 current source were used for spraying. Atmospheric air was used as plasma-forming gas. Spraying process parameters: voltage - 200V, current -170A, nozzle cut distance from base - lOOmm.

The thickness of the applied coating was 20-30 microns.

The resulting coating was heat treated in a SNOL furnace at 560 ° C for 2 hours and cooled in air.

Other performance examples and the resulting coating characteristics are given in Tables 1 and 2.

Key catalyst operating characteristics are the catalyst ignition temperature and the carbon monoxide (CO) full conversion temperature.

The main reaction used to determine the characteristics of the catalyst is the oxidation of carbon monoxide (CO) with oxygen (O2) to carbon monoxide (CO2). The catalyst ignition temperature is the temperature at which 50% of the oxidation of carbon monoxide (CO) occurs to carbon monoxide (CO2). The full conversion temperature is the temperature at which 100% oxidation of carbon monoxide (CO) to carbon monoxide (CO2) occurs. These characteristics can be determined by laboratory and bench tests. In our case, the characteristics were determined by bench tests.

Table 2 shows the results of tests for catalytic coatings containing various transition metal oxides in a carbon monoxide oxidation reaction.

The table shows that the use of transition metal oxides as catalysts is quite effective, with a full conversion temperature of carbon oxide not exceeding 300 ° C and a catalyst ignition temperature readable as a characteristic of catalyst activity in the range 150-180 ° C (prototype not less 250 ° C).

In addition, Table 2 shows that the use of a complex mixture of transition metal oxides increases the catalyst activity as seen in Examples 4, 5 and 6.

The high dispersion of the powder mixture used in the new invention (at least 100 microns) increases the utilization rate of the powder while making it much more economical to use.

* Table 7

Copper oxide, % by weight 1 o 1 m Ό cn O Nickel oxide, % by weight 1 cu 00 cu CU cu 1 Cobalt oxide,% by weight 1 cn cu Iron oxide,% by weight 1 00 00 1 cu uo Manganese oxide,% by weight t 1 v © Ό 1 1 1 Tungsten mo oxide,% by weight CO 1 1 m m cn o Molibde no oxide,% by weight m 1 1 m m cn KO Chromium oxide,% by weight cu 1 1 cu 1 Vanadium oxide by weight CU 1 1 1 cu cu Aluminum hydroxide,% by weight remaining quantity remaining quantity remaining quantity remaining quantity In the remaining amount remaining quantity remaining quantity Aluminum,% by weight m ΙΛ o, Λ .Λ &, N O · £, - cu m Γ'-

CO complete conversion temperature ° C 300 | 280 | 300 o o cu 260 260 290 Ignition temperature ° C 081 1,170 | 170 o vO 165 150 180 Position from Table 1 - cu cn and o r-

Claims (3)

DEFINITION OF INVENTION 1. A process for the preparation of a composite catalytic coating comprising the step of depositing a porous coating of aluminum and / or titanium, aluminum and / or titanium oxides and aluminum and / or titanium hydroxides on a substrate by a plasma spraying process, characterized in that transition metal oxides are added to the powder composition. powder as a substance with catalytic properties at the following weight percentages: Aluminum and / or titanium metal 1 - 7 Oxides of aluminum and / or titanium 0,1-12 Oxides of transition metal 1 - 30 Hydroxides of aluminum and / or titanium Process for the preparation of a composite catalytic coating according to claim 1, characterized in that vanadium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel and copper are used as transition metal oxides. 3. A process for the preparation of a composite catalytic coating according to claims 1 and 2, wherein the resulting mixture has a powder dispersion of at least 100 microns.